kinematic viscosity definition wikipedia

In 1932, Hohenemser and Prager proposed the first model for slow viscoplastic flow. In 1934, Odqvist generalized Norton's law to the multi-axial case.Ĭoncepts such as the normality of plastic flow to the yield surface and flow rules for plasticity were introduced by Prandtl (1924) and Reuss (1930). In 1929, Norton developed a one-dimensional dashpot model which linked the rate of secondary creep to the stress. In viscoplasticity, the development of a mathematical model heads back to 1910 with the representation of primary creep by Andrade's law. An improved plasticity model was presented in 1913 by Von Mises which is now referred to as the von Mises yield criterion. Research on plasticity theories started in 1864 with the work of Henri Tresca, Saint Venant (1870) and Levy (1871) on the maximum shear criterion. dynamic problems and systems exposed to high strain rates.systems exposed to high temperatures such as turbines in engines, e.g.the prediction of the plastic collapse of structures,.the calculation of permanent deformations,.In general, viscoplasticity theories are useful in areas such as: For polymers, wood, and bitumen, the theory of viscoplasticity is required to describe behavior beyond the limit of elasticity or viscoelasticity. However, certain alloys exhibit viscoplasticity at room temperature (300K). The mechanism usually becomes dominant at temperatures greater than approximately one third of the absolute melting temperature. An alternative approach is to add a strain rate dependence to the yield stress and use the techniques of rate independent plasticity to calculate the response of a material įor metals and alloys, viscoplasticity is the macroscopic behavior caused by a mechanism linked to the movement of dislocations in grains, with superposed effects of inter-crystalline gliding. The yield surface is usually assumed not to be rate-dependent in such models. In these models, the stress is allowed to increase beyond the rate-independent yield surface upon application of a load and then allowed to relax back to the yield surface over time. Viscoplasticity is usually modeled in three-dimensions using overstress models of the Perzyna or Duvaut-Lions types. The sliding element can have a yield stress (σ y) that is strain rate dependent, or even constant, as shown in Figure 1c. In the figure E is the modulus of elasticity, λ is the viscosity parameter and N is a power-law type parameter that represents non-linear dashpot. Plasticity can be accounted for by adding sliding frictional elements as shown in Figure 1.

Rate-dependence can be represented by nonlinear dashpot elements in a manner similar to viscoelasticity. The elastic response of viscoplastic materials can be represented in one-dimension by Hookean spring elements. The main difference between rate-independent plastic and viscoplastic material models is that the latter exhibit not only permanent deformations after the application of loads but continue to undergo a creep flow as a function of time under the influence of the applied load. Rate-dependent plasticity is important for transient plasticity calculations. The inelastic behavior that is the subject of viscoplasticity is plastic deformation which means that the material undergoes unrecoverable deformations when a load level is reached. Rate-dependence in this context means that the deformation of the material depends on the rate at which loads are applied. Viscoplasticity is a theory in continuum mechanics that describes the rate-dependent inelastic behavior of solids. Elements used in one-dimensional models of viscoplastic materials.

Kinematic viscosity definition wikipedia